The invention relates generally to an exoskeleton, a device worn by a person to augment physical abilities. Exoskeletons can be considered passive or active. Passive devices do not require an energy source, such as a battery. Active devices require an energy source to power electronics and usually one or many actuators. It is desirable for exoskeletons to be as lightweight as possible, since the user must carry and move the device along with the body. It is also desirable for these devices to be capable of providing large amounts of force, torque and/or power to the human body in order to assist with motion. These two requirements of low mass and high force/torque/power are often competing requirements and design tradeoffs must be made. Furthermore, it is difficult to apply large forces and torques to the human body. The musculoskeletal system of the human body is capable of sustaining incredible amounts of torque and force, but the exterior of the body is not accustomed to withstanding similar magnitudes of force/torque. Along with being lightweight, and capable of producing high forces/torques/powers, exoskeletons should also be comfortable and efficient at transferring energy to the human. Furthermore, the device should not interfere with the natural range of motion of the body.
It is also desirable for active exoskeletons to be energy efficient and easily controlled. Active exoskeletons require an energy source to power electronics, sensors and usually actuators. Typically, batteries are used with electric motors. However, compressed air can also be used to power pneumatic exoskeletons. The exoskeleton should be as efficient as possible at converting the energy source into useful mechanical force/torque/power. Since the user is often required to also carry the energy source, an efficient device results in a lighter device, a primary design objective. Onboard electronics allow designers to control the exoskeleton, but the device can be mechanically designed to allow for easier control. For example, active devices with a lower transmission ratio are often easier to control and back drive. Output force and torque sensors can also be used to make controlling easier.